Submersed Aquatic Vegetation Restoration and Management from the Biologist and Resource Perspective

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1 Submersed Aquatic Vegetation Restoration and Management from the Biologist and Resource Perspective Carol Franze, LA Sea Grant/LSU AgCenter and Michael Poirrier, University of New Orleans

2 Presentation Outline General Characteristics of Lake Pontchartrain Environmental Impacts Restoration and Remediation Measures SAV Historic Changes in the Basin Impacts to Distribution and Abundance Rangia Clam Benefits and Restoration Lessons Learned Source Populations

3 From: Environmental Atlas of the Pontchartrain Basi

4 General Characteristics of Lake Pontchartrain Size: 1,630 km 2. Depth: 3.7 m. Salinity: 4 ppt SAV dominated by Vallisneria americana & Ruppia maritima Benthos: dominated by Rangia clams Fisheries: Blue crab, Peneid Shrimps & Estuarine Finfish Origin: Formed by deltas of the Mississippi River (approx. 5,000 BP) Freshwater from rivers and streams along the Northshore Tidally influenced through Rigolets and Chef Menteur Passes

5 Priority Habitats in the Upper and Middle Pontchartrain Basin

6 Factors that affect SAV abundance Available light controls maximum depth and abundance Nutrients can increase density, but dissolved nutrients can also limit growth by increasing shading by algal epiphytes and phytoplankton Algal epiphyte grazers are important in controlling overgrowth

7 proportion ppt Salinity: factor in Species Composition S pecies composition and mean annual salinity Freshwater species Ruppia S alinity

8 Major Environmental Issues Shell Dredging

9 Major Environmental Impacts Sewerage and urban runoff Agricultural runoff Mississippi R. Gulf Outlet: saltwater intrusion, salinity stratification and associated hypoxia Subsidence: wetland loss and shoreline retreat Highly modified shoreline (about 50%): armoring Shell dredging: 1933 to 1990 Bonnet Carré Spillway: MSR flood control Tropical Storm Events: increased salinity and erosion El Nino, La Nina and Sea Level Rise

10 Restoration and Remediation Measures Study to Restore Lake Pontchartrain 1989, stating economic benefits of restoration Formation of the Lake Pontchartrain Basin Foundation Ban on Shell Dredging, 1990 Dairy Retention Ponds Improvements in Storm Water Runoff from Urban Areas Marsh, Swamp Preservation and Restoration Projects Additional Wildlife Refuges

11 Results from Ban on Shell Dredging

12 Historic Changes in SAV in the Lake Pontchartrain Survey Areal Cover (ha) Autocad Corrected (ha) Patch Corrected (ha) Net change (%) Suttkus et al.( ) ? Montz (1973) Mayer (1985) Burns et al. ( ) Cho and Poirrier (2000) (north shore only)

13 SAV Transect Data H. Georges H. Katrina Bonnet Carre Opening La Nina Drought

14 Vallisneria Response to Habitat Change Decreased with increasing salinity Can tolerate low light levels Mature beds can tolerate wave energy Slow colonization of new sites Transplanting can enhance restoration Beds more stable than Ruppia

15 Ruppia Response to Habitat Change Great seasonal and annual variation in coverage and biomass Seeds important in lifecycle Masses of drifting plants important in seed dispersal Requires more light than Vallisneria Less resistant to wave energy than Vallisneria Rapid dispersal and growth under appropriate conditions without transplanting

16 Rangia cuneata clams Occur in low salinity estuaries (< 15 ppt) Atlantic & Gulf of Mexico Keystone species in Lake Pontchartrain, abundant, serve as food for fish, ducks, blue crab, and other animals. Shells provide hard substratum. Filter feeding regulates turbidity. Shell dredging from 1933 to 1990, gravel substitute, peaked in late 1970 s with an annual economic value of $34 million.

17 Recovery from Shell Dredging Rangia Clam Density Change Bonnet Carre opening H. Georges La Nina driven Drought H. Katrina

18 Reestablish Rangia and diverse benthic community

19 SAV Restoration by Transplanting High energy environment, a bad storm can make any method or time inappropriate. Low water levels can damage transplants and even mature plants. Enclosures don t provide protection from high wave energy or many SAV grazers. Microhabitat dynamics such as, depth, sediment and wave energy are important. Best results were obtained when greenhouse plants were grown in coconut fiber mats or peat pots until roots and rhizomes developed.

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21 SAV Habitat SAV distribution and abundance is very dynamic. Shifts occur in species composition and abundance with El Niño & La Niña climate patterns. Salinity controls species composition. Water clarity, dispersal and colonization control abundance. New transplants and a developing community not as resilient as a mature meadow. Density matters. Shellfish restoration contributes to SAV restoration.

22 Lessons Learned SAV adaptations and limiting factors are vastly different from marsh plants SAV loss with nutrient additions does not always apply to freshwater but does apply to estuarine and marine habitats Potential Habitat Models and historic data about past distribution are important in the restoration of species with seasonal life cycles Restoration by transplanting only works if habitat is restored first

23 Lessons Learned SAV mapping is appropriate for persistent species, but not dynamic species with seasonal and annual variation Maintaining and restoring source populations and dispersal processes are important restoration strategies Natural dispersal of seeds and other propagules by manatee, turtles, water fowl and fish can be increased by holistic restoration

24 Photograph by Tom Carlise, USFWS Source Populations

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